1. Field of the Invention
The present invention relates to radio transmissions and in particular it concerns a method and apparatus for transmitting/receiving STM-4 (SDH) or STS-12 (SONET) digital signals over two RF carriers in a respective SDH or SONET radio regenerator section.
2. Description of the Prior Art
In present telecommunication systems, the need often arises (particularly with operators who have to manage congestioned networks) of providing high capacity radio systems with high spectrum efficiency and not much complex architecture. These radio systems are required to transmit high order digital signals, such as STM-4 (SDH) or STS-12 (SONET) synchronous hierarchy levels, at 622.08 Mb/s. Such links must be capable of being inserted in optical networks on STM-4 interface nodes with all the features of performance monitoring, management, protection, etc . . . The above needs are also apparent from the last issues of some ETSI Recommandations.
The solution which is at present known for interconnecting an STM-4 data stream with a radio equipment provides for the transmission of four STM-1 signals over four corresponding RF carriers. In essence, it is a solution providing for the transmission of four STM-1 signals in the radio section and allows the transport of an STM-4 stream in a regenerator section, by using four RF carriers in a 4+2 protection system configuration.
It is clear that this type of approach does not optimize the spectral efficiency of the transmission system. Moreover, it requires the use, in the radio link, of four transceivers (in addition to two spare transceivers) and the management of four STM-1 channels in a minimal configuration of the protection system that contemplates the use of two protection channels (4+2 protection).